Hi all,
I wanted to share how I finally found several vacuum leaks in my 74 engined car, after spraying carb cleaner/ propane/ wd40 didn't detect anything. Tony (boyt911sc) on this forum suggested a pressure test so I wanted to see if a regular household vacuum cleaner would work as the source of pressure. Well, it does!
I took off the bag and connected the hose at the 'exhaust' end of the vacuum using overlapping strips of electrical tape to make this mostly airtight. I also taped over the hole where the power cable comes out - basically you need tape over anywhere you can feel air blowing out.
I then took off the rubber boot off the air meter/ throttle assembly and made a connector using the end of a plastic soda bottle to join the end of the vacuum's hose to the throttle intake, sealing things with masking tape.
Well, switching on the vacuum even at low power created plenty of pressure. I mixed washing up liquid with a bit of water in a sprayer and went over everything that carries air. Oh, don't forget the tennis ball in the exhaust. I found big bubbling action at 2 of the injector seals and at the pop off valve too. Now obviously it's tricky to access everywhere with the engine in the car but I think for the very little effort required, this approach is pretty good!
For reference the problem I was trying to solve was a 2 to 3k rpm bucking. Otherwise the car starts and runs well and fuel pressure and ignition tests have all been done first.
Best,
Thomas